24 research outputs found
Coherent spin radiation by magnetic nanomolecules and nanoclusters
The peculiarities of coherent spin radiation by magnetic nanomolecules is
investigated by means of numerical simulation. The consideration is based on a
microscopic Hamiltonian taking into account realistic dipole interactions.
Superradiance can be realized only when the molecular sample is coupled to a
resonant electric circuit. The feedback mechanism allows for the achievement of
a fast spin reversal time and large radiation intensity. The influence on the
level of radiation, caused by sample shape and orientation, is analysed. The
most powerful coherent radiation is found to occur for an elongated sample
directed along the resonator magnetic field.Comment: Latex file, 11 figure
Matching Regge Theory to the OPE
The spectra of masses and decay constants for non-strange meson resonances in
the energy range 0--2.5 GeV is analyzed. It is known from meson phenomenology
that for given quantum numbers these spectra approximately follow linear
trajectories with a universal slope. These facts can be understood in terms of
an effective string description for QCD. For light meson states the
trajectories deviate noticeably from the linear behavior. We investigate the
possible corrections to the linear trajectories by matching two-point
correlators of quark currents to the Operator Product Expansion (OPE). We find
that the allowed modifications to the linear Regge behavior must decrease
rapidly with the principal quantum number. After fitting the lightest states in
each channel and certain low-energy constants the whole spectrum for meson
masses and residues is obtained in a satisfactory agreement with phenomenology.
We briefly speculate on possible implications for the QCD effective string.Comment: 24 pages, Latex, significant changes in discussion of fits, more refs
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Photon-assisted tunneling in a Fe8 Single-Molecule Magnet
The low temperature spin dynamics of a Fe8 Single-Molecule Magnet was studied
under circularly polarized electromagnetic radiation allowing us to establish
clearly photon-assisted tunneling. This effect, while linear at low power,
becomes highly non-linear above a relatively low power threshold. This
non-linearity is attributed to the nature of the coupling of the sample to the
thermostat.These results are of great importance if such systems are to be used
as quantum computers.Comment: 4 pages, 4 figure